The alpha operon ribosome binding site in bacteria is surrounded by this complex pseudoknot

Pseudoknot

A pseudoknot is a nucleic acid secondary structure containing at least two stem-loop structures in which half of one stem is intercalated between the two halves of another stem. The pseudoknot was first recognized in the turnip yellow mosaic virus in 1982...

ted RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 structure. Translation of the mRNA produces 4 ribosomal protein

Ribosomal protein

A ribosomal protein is any of the proteins that, in conjunction with rRNA, make up the ribosomal subunits involved in the cellular process of translation. A large part of the knowledge about these organic molecules has come from the study of E. coli ribosomes. Most ribosomic proteins have been...

 products, one of which (S4) acts as a translational repressor by binding to the nested pseudoknot region. The mechanism of repression is thought to involve a conformational switch in the pseudoknot region and ribosome

Ribosome

A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....

entrapment.